Certain newly developed seismic techniques involve distribution of arrays of cables on the seafloor. Previously, cables laid on the floor of a body of water have been subject to damage when fishing boats would entangle the cable in their nets or other fishing equipment. Prior techniques for laying/burying cable involved very large boats which handled the spool of cable to be laid on the seafloor on the back of the deck. The boat would pull a plow and the cable would extend from the boat deck to the plow on the seafloor. Because of this method of installation/burying of the cable, the cable weight, suspended between the plow on the seafloor and the back deck of the boat, put significant stresses on the cable so that it had to be strengthened so that it could withstand the applied stresses from its own weight. As a result, the cable became very expensive due to the modifications it required to have sufficient structural strength to withstand the stresses from its own weight. Additionally, because of the heavier-duty design of the cable, the weight of the entire spool on the back of the boat further made it necessary to use much larger boats than would have otherwise been necessary had the cable been of a lighter-duty construction. In many such seismic applications, an array of multiple strands of cable must be arranged on or below the seafloor, with one end of the cable extending to a buoy or production facility. Thus, the draw-backs of prior techniques would involve expensive cables to withstand the structural stresses from suspending the cable from the boat to the plow, as well as the need for use of larger vessels than would have otherwise been necessary, had the cable simply been of a lighter-duty design.
Thus, it is an objective of the present invention to provide a technique and equipment so that the cable does not need to be unnecessarily strengthened to withstand its own weight suspended from the surface to the seafloor. With the technique of the present invention, lighter-duty boats can be used because the cable weighs less and the method for its distribution facilitates the process of creating the desired grid on the seafloor to accommodate seismic data gathering from the formations below. This technique is applicable as well to other situations where cable must be laid economically for a variety of different purposes.
Plows that lay and bury cable from a spool on the deck of a boat are known. Various versions of such plows are made by J. Ray McDermott Co., as well as American Telephone & Telegraph Company, Soil Machine Dynamics, and others.
Those of skill in the art will get a better appreciation of the apparatus and method from a review of the preferred embodiment described below.